Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $59.33   4.723%   $62.1322   $62.13   $62.15   $62.10  
  Purchase #2 $120.33   12.173%   $134.9778   $134.98   $135.00   $135.00  
  Purchase #3 $191.95   13.434%   $217.7366   $217.74   $217.75   $217.70  
  Purchase #4 $95.83   10.608%   $105.9956   $106.00   $106.00   $106.00  
  Purchase #5 $171.77   9.463%   $188.0246   $188.02   $188.00   $188.00  
  Purchase #6 $120.57   12.548%   $135.6991   $135.70   $135.70   $135.70  
  Purchase #7 $99.91   12.380%   $112.2789   $112.28   $112.30   $112.30  
  7 purchase totals = $859.69       $956.8448   $956.85   $956.90   $956.80